Many olefin polymerization catalysts are known, including conventional Ziegler-Natta catalysts. While these catalysts are inexpensive, they exhibit low activity and are generally poor at incorporating α-olefin comonomers. To improve polymer properties, single-site catalysts, in particular metallocenes are beginning to replace Ziegler-Natta catalysts.
Catalyst precursors that incorporate a transition metal and an indenoindolyl ligand are known. U.S. Pat. Nos. 6,232,260 and 6,451,724 disclose the use of transition metal catalysts based upon indenoindolyl ligands.
PCT Int. Appl. WO 01/53360 discloses open architecture indenoindolyl catalysts that may be supported on an inert support. U.S. Pat. No. 6,559,251 discloses a process for polymerizing olefins with a silica-supported, indenoindolyl Group 4-6 transition metal complex having open architecture. U.S. Pat. No. 6,211,311 teaches that many heterometallocenes are inherently unstable and this causes difficulties in supporting these catalysts; in particular, poor catalyst activity often results. This problem is avoided by using chemically treated supports to prepare supported catalysts containing heteroatomic ligands.
U.S. Pat. No. 6,541,583 discloses a process for polymerizing propylene in the presence of a Group 3-5 transition metal catalyst that has two non-bridged indenoindolyl ligands. Pending application Ser. No. 10/123,774, filed Apr. 16, 2002, discloses a process for polymerizing ethylene in the presence of a silica-supported Group 3-10 transition metal catalyst that has two bridged indenoindolyl ligands to obtain “ultra-high” molecular weight polyethylenes.
Despite the considerable research done on indenoindolyl complexes, there has been no indication of the importance of the substituent on the indole nitrogen. In the prior work, methyl or phenyl is the typical substituent although ethyl and trimethylsilyl have also been used. U.S. Pat. No. 6,451,724 describes the substituent on the indole nitrogen broadly for the bridged complexes. However, the reference gives no indication of the importance of indole substituents, and the examples have only methyl and phenyl substituents.
Non-bridged indenoindolyl complexes are easier to synthesize but give lower molecular weight (higher melt index) than their bridged counterparts. The need continues, however, for new ways to make polyolefins with increased molecular weight. Molecular weight affects several properties such as impact and toughness. For certain applications, high molecular weight polyolefins are required. The industry would also benefit from the availability of new processes that capitalize on the inherent flexibility of the indenoindolyl framework. When high molecular weight polyolefins are required, bridged complexes have been used. There is a need to be able to prepare high molecular weight polyolefins from the more available non-bridged indenoindolyl complexes.